Thermal printers are used increasingly in retail, warehouse, and other locations to generate adhesive labels for marking goods to facilitate identification, tracking, and pricing. Due to the print quality, accuracy, and versatility of dot matrix or array type thermal print mechanisms, a wide variety of information can be produced quickly and inexpensively on the labels as the need arises. Lot sizes of labels can be as small as one or as large as several hundred or more, depending upon the particular application. Printer electronics integral with the printer may include a microprocessor, memory, and associated internal and external communications so that the printer can be used to create alphanumeric characters of varying size, font, and orientation, stylized graphical markings such as logotypes and trademarks, and machine readable indicia such as bar codes for the particular goods to be labeled. A variety of these characters, markings, and indicia can be printed in combination on a single label.
Thermal printers can print on thermal paper which darkens or changes color when heated above a threshold temperature by the thermal print mechanism or printer head. By selectively activating discrete thermal elements in the printer head array as the thermal paper passes by, the desired information can be reproduced on the thermal paper. To provide intimate, uniform contact between the printer head and the label, the label is passed typically through a nip formed by the printer head and a powered rubber platen roller. The platen may be used to drive the label through the nip. Instead of heating the label, a thermal transfer ribbon having a layer of dried ink on a thin backing sheet can be disposed between the printer head and a paper label on the platen. As the printer head is heated above the ribbon ink threshold temperature, the ink melts and is transferred to the label where it dries and forms an indelible marking of the desired information.
"Label stock" generally includes a series of printable surfaces of paper or other label material adhesively and releasably attached to a web carrier backing. The label stock typically is manufactured in roll form for continuous feeding through a thermal printer. "Linerless" label stock is also commercially available which is in the form of a roll of continuous adhesive strip. Special handling of this stock is required to prevent misfeeding and jamming of the thermal printer. For example, a silicone platen roller may be used to prevent adhesion of the stock thereto and a cutter mechanism may be provided to separate a printed label portion from the remaining roll.
In printers for printing on a series of labels adhered to a web, it may be desirable to dispense printed labels individually, wholly or partially delaminated from the web, to facilitate removal by an operator. By passing the web across a peeler bar at an acute angle after discharge from the nip formed between the printer head and platen, a leading edge of the label becomes delaminated or detached from the web. An additional roller may be provided biased against the platen or other roller to form a second nip through which solely the web passes. By keeping the web taut and maintaining close conformance of the web to the peeler bar, reliable dispensing of the printed labels may be ensured.
When initially threading the printer with the label stock, the stock must be passed through the printer head nip and, if the peeler bar is to be used, the web also must be passed through the roller nip. The web should be taut between the printer head nip and the roller nip to tightly conform the web to the peeler bar. Various arrangements are known for providing a gap between the printer head and platen to facilitate loading. For example, see U.S. Pat. Nos. 5,014,073 and 5,150,130. Known arrangements for providing a gap between a roller and a platen to facilitate removal of paper jams include the arrangement disclosed in U.S. Pat. No. 4,947,185. Arrangements that require manual actuation to provide a gap between the roller and the platen include a spring loaded roller with bi-stable positioning so that the roller is stable in positions both against the platen as well as spaced therefrom. Manual actuation is required both to displace the roller from the platen as well as return the roller to the contact position. Each of these arrangements entails separate apparatus for displacing a printer head and a roller from the platen.